A magnetic sheet pack is used as a recording medium for electronic cameras or the like. Referring to FIG. 8, a magnetic sheet pack 01 comprises a flexible magnetic sheet 03 contained in a pack 02. In a production process for such a magnetic sheet pack 01, there is a step so-called "burnishing". In the burnishing work, the magnetic sheet is rotated and a scraper is contacted against the surface of magnetic material of the rotating magnetic sheet. This grinds off lumps of magnetic material powder projecting from the surface which are formed during coating of the magnetic material powder, thereby obtaining a smooth surface of a magnetic floppy disk.
A prior art burnishing work will be briefly described with reference to FIG. 9. Referring to FIG. 9, a magnetic sheet 1 is rotated (in the direction indicated by an arrow A) by a rotational drive unit of a polishing device, and a sapphire chip as a scraper is attached to a base plate 3 at an end of a head carriage of the polishing device. The sapphire chip 2 has the same shape as a normal magnetic head, with a slightly curved sliding surface 2a, and both an angle .theta.1 between an upstream side surface 2b and a magnetic material surface 1a and an angle .theta.2 between a downstream side surface 2c and the magnetic material surface 1a are about 10 to 20 degrees.
When the sapphire chip 2 is moved in the radial direction of the magnetic sheet 1 while the magnetic sheet 1 is rotated, magnetic lumps projecting from the magnetic material surface 1a are ground off by the sapphire chip 2 to smooth the magnetic material surface 1a.
Magnetic tapes and sheets are normally processed by a calender to obtain smooth surfaces, thus enabling short wavelength recording. It is the object of burnishing to remove small irregularities or discrete projections which are present even after calendering, thus reducing dropouts generated before punching and making the magnetic sheet less abrasive.
The prior art method shown in FIG. 9, however, has a problem in that scraped magnetic powder 4 accumulates on the downstream side surface 2c, and the accumulated magnetic powder 4 may attach again to the magnetic material surface 1a. The attached magnetic powder 4, after one turn of the magnetic sheet, comes in between the upstream side surface 2b and the magnetic sheet and strongly adheres to this part of the magnetic sheet. When the track including this part of the magnetic sheet is used for recording or reproduction, the magnetic head jumps up from the magnetic material surface 1a due to the presence of the stuck lump of magnetic powder 4, and poor contact of the head and a dropout will result.